1. Field of the Invention
This application relates generally to the deposition of silicon-containing materials in semiconductor processing. More particularly, this application relates to the selective deposition of silicon-containing films.
2. Description of the Related Art
It is often desirable to selectively deposit silicon on semiconductor surfaces without depositing on insulating surfaces. For example, heterojunction bipolar transistors are often fabricated using selective deposition techniques that deposit epitaxially-deposited single-crystal, e.g., semiconductor films only on active areas. Other transistor designs benefit from elevated source/drain structures, which provide additional silicon that can be consumed by the source/drain contact process without altering shallow junction device performance. Selective epitaxy on source/drain regions advantageously reduces the need for subsequent patterning and etch steps. Generally speaking, selective deposition takes advantage of differential nucleation during deposition on disparate materials. The precursor of choice will generally have a tendency to nucleate and grow more rapidly on one surface and less rapidly on another surface. At the beginning of a nucleation stage, discontinuous films on oxide have a high exposed surface area relative to merged, continuous films on silicon. Accordingly, an etchant added to the process will have a greater effect upon the poorly nucleating film on the oxide as compared to the rapidly nucleating film on the silicon. The relative selectivity of a process can thus be tuned by adjusting factors that affect the deposition rate, such as precursor flow rates, temperature, pressure and the rate of etching, such as etchant flow rate, temperature, pressure. Changes in each variable will generally have different effects upon etch rate and deposition rate. Typically, a selective deposition process is tuned to produce the highest deposition rate feasible on the window of interest while accomplishing no deposition in the field regions.
Selective deposition of semiconductors is of considerable commercial importance for a variety of industrial applications. Thus, there is a need for improved methods to selectively deposit silicon onto semiconductor surfaces.